The supply side: two lines and two valves
Hot and cold water reach the faucet through flexible supply lines. Each has a small shutoff valve under the sink, often called an angle stop. Know where they are. Turning them clockwise stops water to the faucet without shutting off the house.
These valves are cheap and sit unused for years, which means they often seize. If yours will not close, replace them before you need them. A stuck valve in an emergency turns a small leak into a flood.
The drain side: basket, trap and branch
Water leaves through the strainer basket into the tailpipe and into a curved section called the P-trap. The trap holds a plug of water that blocks sewer gas from coming up the drain. From the trap, the pipe runs to the wall and joins the branch line.
Most clogs happen here. Grease, food and soap collect in the trap. Unscrewing it over a bucket and cleaning it clears many clogs. If the clog is past the trap, the branch line needs a cable, see drain cleaning.
Parts under a kitchen sink
| Part | What it does | Common problem |
|---|---|---|
| Angle stop valves | Shut off water to the faucet | Seized or leaking |
| Supply lines | Carry water to the faucet | Worn or kinked |
| P-trap | Holds water to block sewer gas | Clogs and slow leaks at the joints |
| Tailpipe and branch | Carry waste to the wall | Grease buildup |
| Vent | Lets air in so the drain flows | Slow draining or gurgling |
The dishwasher and disposal connections
A dishwasher drains through a hose that connects to the disposal or to the sink tailpipe. To keep dirty water from flowing back, the hose is looped high under the counter or connects through an air gap on the sink deck. Which one is required depends on code, so ask when you remodel.
A garbage disposal sits below the sink basket and discharges into the trap. If the dishwasher backs up into the sink, the disposal or the drain past it is usually partly clogged. A jammed disposal needs a different fix, see garbage disposal repair.
Water under the sink?
Call and tell us where it is coming from. We can help you decide what to shut off.
Quick checks for common kitchen sink problems
- Slow drain: clean the trap and strainer first, then run hot water
- Gurgling: may be a vent problem, so check whether other fixtures gurgle too
- Leak at the trap: tighten the slip nuts by hand and check the washers
- Leak from the supply line: close the angle stop and replace the line
- Smell: dry trap or a dirty disposal, run water and clean the splash guard
Why vents matter under the counter
A sink drain needs air behind the water. Without a vent, the draining water can pull the water seal out of the trap, and the sink gurgles or smells. The vent usually rises inside the wall and joins a larger vent or exits through the roof.
Some remodels use an air admittance valve under the sink when a conventional vent is hard to reach. Whether one is allowed depends on code, so check before you plan a layout around one.
Layout problems that cause repeat clogs
Long horizontal runs, too little slope and sharp turns slow the flow and collect grease. A tailpipe that dips below the trap inlet or a trap installed backward also causes trouble. These faults are common in kitchens that were remodeled without a plumber.
If your kitchen sink clogs again and again, the layout may be the cause, not the food. A plumber can look at the arrangement and a camera can show whether the branch line has a low spot.
Annual under-sink check
- Open both angle stops and close them again to keep them working
- Look for green or white crust at joints, which means a slow leak
- Feel braided supply lines for bulges or fraying
- Run the dishwasher and watch the drain connections
- Check the cabinet floor for soft or stained wood
- Clean the strainer and disposal splash guard
Kitchen sinks in Bothell homes
Bothell has homes from every decade since the 1950s, and kitchens in the older ones have often been remodeled without a full plumbing update. It is common to find a mix of metal and plastic drain pipe under the sink, with old angle stops that no longer close.
The City Permit Center says some plumbing work needs a permit. Bothell Municipal Code exempts certain repairs, such as stopping a leak or replacing a prefabricated fixture. Moving a sink or adding a dishwasher is a different story. For a new fixture or a remodel, see plumbing installation. We serve Kenmore and nearby towns on our service areas page.
Traps, vents and dishwasher drain connections follow the Uniform Plumbing Code (UPC) as adopted in Washington under WAC 51-56.
Kitchen sink plumbing questions
A dry trap, food in the disposal or a partly clogged drain can all cause it. Run water, clean the strainer and the disposal splash guard. If it persists, the line may need cleaning.
It depends on the code that applies to your installation. Ask us or the Permit Center. Many dishwashers use a high loop instead.
The drain is partly blocked or the vent is not letting in air. If it is only the kitchen, a cable may fix it.
Many people can, but old shutoff valves often fail. Replace them first. If the valves will not close, call us.
It is likely the air gap for the dishwasher drain. It sits above the sink so dirty water cannot flow back.
Keep grease out, use a strainer and run hot water after washing. Avoid putting fibrous food in the disposal.